The invention relates to a ring illumination device for an objective, particularly for a microscope objective, and a microscope objective with such a ring illumination device.
Various illuminating devices and illuminating technologies for microscopes are known, from the prior art. Ring illumination devices are used primarily for dark field reflected light illumination. Known systems are disposed outside the image-forming optics of the objective. The light is deflected onto the sample generally by a ring-shaped mirror or ring-shaped lenses. The designs tend to be costly and to occupy a large space outside the objective, which can have the effect of, e.g., substantially inhibiting the radius of swing of the objective.
In U.S. Pat. No. 4,186,993 A, for example, an objective is described wherein a ring-shaped transparent diffuser and a ring-shaped condenser lens are disposed around the image-forming optics, in the light-spreading direction.
In U.S. Pat. No. 4,626,079 A a number of variants of a dark field illumination system are shown, wherein a combination of ring-shaped lenses and/or ring-shaped mirrors are employed around the objective lens.
DE 603030328 T2 shows a ring-shaped illumination device for microscopes wherein LEDs are used as light sources. Two or three types of LEDs with different emission colors, preferably red, green, and blue, are used, which are disposed in the same play around the optical axis and are oriented essentially perpendicularly to the optical axis. The color components are mixed using dichroic mirror groups, and are deflected onto the object plane by means of a reflector.
In DE 20-2005-004635 U1 discloses an illumination ring for a reflected light microscope having at least movably mounted LEDs which have their adjustment angle relative to the optical axis adjustable for the purpose of focusing of the illumination. Because of thermal sensitivity, the LEDs are operated at at most one half of the admissible current, and the necessary light intensity is achieved by focusing or by using a larger number of LEDs. The contacting and electricity supply to the LEDs are relatively costly.
CN 101414056 B discloses an objective with a dark field illumination device. The image-forming optics of the objective are disposed in an inner cylinder, with an LED illumination device being disposed in an outer cylinder. Between the LEDs and the object, a ring-shaped optical element is provided which transforms the LED light into parallel light. The illumination device can be coupled to a light field objective also, with a corresponding adapter.
The brightness of an LED increases with the power consumption. At a constant temperature of the semiconductor, the increases is nearly proportional. The efficiency decreases with increasing temperature, however, and therefore the yield of light output at the power limit is reduced, depending on the type of cooling. Thus effective cooling is essential for the efficiency of the illumination.
Accordingly, the underlying problem of the invention was to devise a ring illumination device for reflected light illumination for a microscope objective, and a microscope objective for such an illumination device, which allows dark field illumination with a high light yield and efficiency, and which is easy to set up and requires minimal maintenance.